Grapevine berry development: Understanding environmental and cultural impacts on berry weight loss and shrivelling Prof. Alain Deloire Montpellier University, l'Institut Agro, France

Berry shrivelling is an important phenomenon that occurs through grape berry water loss due to the alteration of the fruit water budget when transpiration and potential water back flow to the plant exceeds the import of water into the berry through the phloem and xylem. Berry shrivelling can have a significant economic impact, reducing yields by up to ≥25% with consequences on berry composition and the resulting wine. Its occurrence and consequences are expected to increase due to predicted climate warming, shifting grape development, and ripening into warmer periods (i.e., heat waves).

Berry fresh mass loss is variable between seasons, sites, and vineyards and it seems to be accelerated by higher temperatures, water constraints and/or stress and excessive bunch sun exposure. Berry shrivelling can occur, before (as early as bloom, affecting the ovaries) or after veraison in red and white varieties.

A recent study on individual Shiraz berries (Montpellier l’Institut Agro vineyard; vines trained in vertical shoot positioning under fertirrigation) revealed interesting and original results comparing normal to shrivelled berries in terms of fresh mass, °Brix, probable alcohol and quantity of sugar per berry (mg/berry). The results clearly demonstrated that the increase in probable alcohol/°Brix per berry (post plateau of berry sugar loading) is not due to berry sugar accumulation during ripening but only to berry water loss. This conforms with previous results on the same cultivar (McCarthy and Coombe 1999; Rogiers et al., 2006; Rogiers and Holzapfel 2015).

Late ripening berry shrivel in Shiraz may begin at around 90 days after flowering, but it is not evident every season. While loss in mesocarp cell vitality and cell membrane integrity precedes the onset of shrivel, the internal biochemical and physiological events that lead to these developmental processes remain largely unknown. However, it was demonstrated that hypoxia (low oxygen) in the berry mesocarp may contribute to the onset of cell death (Xiao et al., 2018a). Previous studies have shown that high temperature and dehydration can exacerbate the extent of cell death and berry dehydration (Bonada et al., 2013; Xiao et al., 2018b), and this can be ameliorated with shade covers (Caravia et al., 2016). It is interesting to note that unlike seeded wine grapes, table grapes do not tend to undergo this late ripening loss in cell vitality. Ultimately, berry shrivelling will affect grape and wine composition and sensory profiles (Suklje et al., 2016).